The field of use of probe systems for measuring physical or chemical measured variables of a medium in process measurements technology is manifold. For example, chemical, foods, biotech or pharmaceutical processes require the use of measuring probes for monitoring the process or a product manufactured in the process. The measuring probes can, for example, be pH-measuring probes, ion-selective electrodes, conductivity probes, turbidity probes, or optical or electrochemical measuring probes for determining a concentration of a substance contained in the process medium to be monitored, such as O2, CO2, certain ion types or organic compounds.
From the state of the art, it is known to perform on process media inline measurements, in the case of which probe systems with an axially movable immersion tube holding a measuring probe come into use. Such probe systems are also referred to as retractable assemblies. These retractable assemblies are secured on a process container, for example, or a pipe conveying the process medium. They have a treatment chamber, into which the measuring probe can be moved temporarily during operation by means of the immersion tube, Into the treatment chamber, different treatment media can be introduced. For example, a rinsing liquid for cleaning the measuring probe can be conveyed through the treatment chamber. Also a supplying of the measuring probe with a sterilization medium, e.g. superheated steam, is possible in the treatment chamber, Finally, also a calibration liquid can be conveyed into the treatment chamber, in order to conduct a calibration of the measuring probe. After termination of the treatment, the measuring probe is moved back into the process container or into the process medium, in order to continue with the inline measurement. In such case, a contamination of the process medium to be monitored, or, conversely, a contamination of the calibration liquid with process medium, is counteracted with the assistance of seals, which seal off the treatment chamber and the process container from one another.
For many processes, especially in foods technology, pharmacy and biotechnology, even slight contaminations from the dissolving out of substances from the process container or medium-contacting parts of the probe system are not tolerable. Other processes, especially also for cleaning the process container, use aggressive media, which can attack the medium-contacting parts of the probe system and lead to undesired corrosion. Chemically resistant materials, with which these problems can be prevented, are, for example, titanium or highly corrosion-resistant nickel-chromium-molybdenum-tungsten alloys. These materials are, however, very expensive. Largely chemically inert synthetic materials, or plastics, such as e.g. PTFE, PFA or PVDF, frequently have a significantly smaller mechanical strength in comparison to metals and metal alloys.
In DE 10 2009 033 558 A1, a probe system of the previously named type is described, which is designed for connection to an Ingold nozzle of a process container. The probe system includes a plug part inserted in the connected state into the Ingold nozzle, which is composed of an outer holding ring, made of metal and securable with a coupling nut on the Ingold nozzle, and, anchored in the holding ring, a plug made of synthetic material and insertable in the Ingold nozzle. The synthetic material of the plug should be suitable for application in aggressive process media, while the metal holding ring should assure a sufficient strength for a robust and stable holding of the retractable assembly by means of the coupling nut.
For cleaning and/or calibrating the measuring probe, the probe system includes a rinsing/washing chamber part, in which a rinsing chamber is placed, which is sealed by seals on the process side against the process medium. In the case of retracting the immersion tube with the measuring probe into the rinsing chamber, it is unavoidable that process medium also gets displaced into the rinsing chamber. Thus, also the rinsing chamber is to be taken into consideration as a medium-contacting end component of the probe system. DE 10 2009 033 558 A1 does not, however, also provide that the rinsing chamber is manufactured from an inert material. In the probe system described there, the rinsing chamber is formed in a sleeve part of the probe assembly, which is secured by means of an additional coupling nut on a pneumatic drive of the immersion tube. For this reason, the sleeve part must be embodied in a relatively solid and mechanically stable form. An embodiment of the sleeve part made of titanium or highly corrosion-resistant materials would, for reasons of cost, be disadvantageous. An embodiment using synthetic material would not assure the required mechanical stability.